Method of increasing the life of gas bubbles

ABSTRACT

Method for coating bubbles of hot gaseous products being injected into cold liquid medium for propulsion for purposes of prolonging the life thereof and enable optimizing release of the energy of the bubbles.

Unite States atem lnvenlor Appl. No. Filed Patented Assignee METHOD OF ENCREASING THE LIFE OF GAS BUBBLES 3 Claims, 5 Drawing Figs.

161. c1 B63h l1/06,

[50] Field of Search 252/307; 117/94; 106/122; 114/665; 115/15; 60/204, 221

[56] References Cited UNITED STATES PATENTS 1,281,670 10/1918 Schmid 252/307 1,421,428 7/1922 Eckelmann 7. 252/307 1,482,383 11/1930 Greider 252/307 Primary Examiner-Leon D. Rosdol Assistant Examiner-W. Schulz Attorneys-Paul A. Frank, Richard R. Brainard, John F.

Ahem, Julius J. Zaskalicky, Frank L. Neuhauser, Oscar B. Waddell and Melvin M. Goldenberg ABSTRACT: Method for coating bubbles of hot gaseous products being injected into cold liquid medium for propulsion for purposes of prolonging the life thereof and enable 0ptimizing release of the energy of the bubbles.

METHOD OF INCREASING THE LIFE OF GAS BUBBLES This application is a continuation of my copending application Ser. No. 476,5 l6, filed Aug. 2, 1965, now abandoned and assigned to the same assignee as the present invention.

My invention relates to gas bubbles, and more particularly to a gas bubble that is thermally insulated to insure an in creased life expectancy thereof.

With two phase propulsors (underwater ramjets) as described in application Ser. No. 439,376, filed Mar. 12, 1965, entitled Propulson by Brown et al., now US. Pat. No. 3,265,027, and assigned to the assignee of the present invention, and other systems which employ the interaction between hot gas bubbles and other fluids, the need arises for a large gas bubble that has a substantially increased life expectancy, so that a significant amount of the energy of the bubble may be conserved as long as possible to be released when the most benefit can be derived therefrom. Ordinary hot gas bubbles have a low life expectancy because of their small size and high heat transfer rate through the liquid comprising the exterior wall of the bubble. If the heat transfer could be substantially reduced, the life of the bubble and its ability to impart its energy more effectively would be greatly improved. Prolonged bubble life greatly improves the efficiency of equipment employing steam or employing the use of the hot gaseous products of a chemical reaction or of combustion, such as the aforementioned two phase propulsor. The need then arises for a large gas bubble having an insulating coating which substantially reduces the loss of heat from within the bubble to increase the life expectancy thereof.

The chief object of my invention is the provision of a gas bubble and a method of making the same that retains the energy therein for a substantially long period of time.

Another object of my invention is the provision of such a bubble that achieves its longevity by having the transfer of heat through its outer surface significantly reduced.

Another object of my invention is the provision of such a bubble which is large and spherically shaped.

A further object of my invention is the provision of a method of applying an insulating coating to the outer surface of a bubble.

These and other objects of my invention will be more readily perceived from the description which follows.

In carrying out the objects of my invention, I provide a hot gas bubble which is coated with a material that thermally insulates the bubble to substantially reduce the loss of heat from within the bubble, so that the life of the bubble and thus the energy contained therein is conserved for a longer period of time than is usually accomplished. Also application of the material to the bubble produces a large, more substantially spherical bubble, for further retaining the heat energy therein.

The attached drawing illustrates preferred embodiments of my invention in which:

FIG. 1 is an enlarged idealized view of one embodiment of a coated bubble of my invention.

FIG. 2 is an enlarged view of another embodiment of my invention.

FIG. 3 is a cross-sectional view of an apparatus for applying coating to a bubble.

FIG. 4 is an alternative mode of the coating apparatus.

FIG. 5 is a further alternative mode of the apparatus of FIG. 4.

In FIG. 1, there is shown an idealized schematic view, greatly enlarged, of a hot gas bubble having a coating in accordance with the present invention. Gas bubble 4, which is a volume or pocket of gas covered by a thin boundary layer of material 2 which retards dissipation of heat from the interior of the bubble to produce a larger bubble, and to thereby significantly increase the length of time during which the bubble exists. Substance 2, which is applied in a variety of ways, as will subsequently be described, comprises a fluid, preferably a liquid such as an oil having a higher viscosity than surrounding liquid 8, preferably a viscosity which is 50 times greater than surrounding liquid 8. Coating material 2 forms a skin or layer that covers the bubble, and thermally insulates the gas 6 in the interior thereof, from the liquid 8, surrounding the bubble. Because of its viscous composition and surface tension, coating material 2 forms in a smooth even layer having a substantially uniform thickness over the entire outside surface area of the bubble. The viscosity of coating 2 is sufficiently high to also damp out motion and oscillation of bubble wall 4, to produce a uniformly curved bubble wall and thereby a sub stantially spherically shaped bubble. Both the motion damping and the spherical shape aid in reducing the loss of heat from gas 6 within the bubble to increase the life of the bubble. Damping reduces heat transfer by limiting both the activity of the bubble in surrounding liquid 8 and the motion of boundary layer 4 surrounding the bubble. The spherical shape reduces the heat transfer area to a minimum. A spherical bubble also has a greater longevity, than an irregularly shaped bubble, because of less tendency for the evenly curved surface of the spherical bubble to be ruptured or broken. Coating material 2 also has a low bonding ability to the surrounding liquid 8, so that it tends to discourage bonding or cohesive action between adjacent bubbles to prevent the formation of irregularly shaped bubbles, which, as aforementioned are undesirable. Coating 2 in acting as a thermal insulator prevents the dissipation of heat energy retained by gas 6, within the bubble, from quickly being dissipated therefrom. The insulating ability in combination with the damping produces a very nearly spherically shaped bubble, as aforementioned, which insures a far greater life expectancy of the bubble; for example, longevity for coated steam bubbles in water is often 0.5 seconds in duration a 150:] gain in bubble life over what is normally obtained.

In systems employing bubbles in combination with another fluid for the generation of power, the longevity of the bubbles, so that energy contained therein is retained for the longest time possible, is of the utmost importance for the successful operation of these systems. The energy may be that due to translation (momentum) of the bubble, or due to the compressive energy (gas pressure) in the bubble. One system, in particular, is the two phase ship propulsion system of Brown et al., aforementioned, wherein gas bubbles and water are mixed and then ejected through a nozzle to produce thrust which drives the ship. It is most important that the bubbles retain the energy contained therein so that they can impart that energy to the water at the instant both the water and bubbles are ejected through the nozzle. If they contract, rupture, or dissipate before being ejected from the nozzle, their effectiveness in propelling the vehicle is substantially impaired. Also, large spherical bubbles, as are produced by my method, e.g., Ainch to xinch in diameter for steam in water, are better adapted to remain intact until the desired energy transfer to the water has taken place. Spherical bubbles also are better adapted to withstand outside forces, which cause irregularly shaped bubbles to be broken quickly. For instance, an oblong, nonspherical, bubble has sections which are significantly weak and subjected to high rupture forces, whereas spherical bubbles are more uniform in strength over their surface area and thus not subject to these same rupturing forces. Thus, because of coating 2, an insulated large, spherical bubble with a substantially increased life expectancy is produced.

Also, when coating 2 is used for bubbles containing condensable gas, the coating may be composed of a material that besides having the aforementioned viscosity and heat transfer characteristics is also nonattractive (nonbonding) to the condensable gas contained in the bubble. By being nonattractive, bubble wall 4 does not aid in condensing gas 6 therein, to thus appreciably extend the life of the bubble.

In FIG. 2, there is shown a gas bubble wherein an alternative mode is employed to prevent early collapse thereof. A volatile substance with a low boiling point and a low heat of vaporization, is employed to cover the bubble. A particularly suitable substance is carbon tetrachloride, CCI which has a boiling point of 76.8 C. and a heat of vaporization of 46.4 calories per gram, as compared with a boiling point of C. for water and heat of vaporization of 540 calories per gram. Thus, it is readily seen that coating substances preferably have boiling points whichare somewhat lower than that of the surrounding liquid, and heats of vaporization also substantially lower than the surrounding liquid. For example, a bubble in water which was covered with CC, had a life of greater than two seconds, as compared with a life of 0.003 seconds for an uncoated bubble. With this mode, the coating substance is applied to the outer wall 12 of bubble 9 to cover all or only part of the outer surface 12 thereof. Coating 10 vaporizes to take up the volume 15 lost through condensation or contraction of the gas 14 from within bubble 9. In other words, substance 10 prolongs the life of the bubble by substituting its own vapor for the gas within the bubble that has dissipated therefrom. The rate at which these volatile substances vaporize is approximately proportional to the rate at which the gas 14 condenses or contracts within the bubble, so that the size of the bubble is kept uniformly large, and also the life of the bubble is thereby significantly increased. Also, heat transfer, as aforementioned, which is a major cause of short bubble life is substantially decreased because the bubble, or a large portion thereof is covered by substance 10 to prevent heat transfer therethrough. Thus, the bubble 5 life is increased twofold, first the volatile substance 10 vaporizes to substitute for the gas volume originally within the bubble that has been lost through condensation or contraction, secondly, the bubble is partially coated in a manner as to substantially prevent heat transfer therethrough. The volatile coating can be of a material nonattractive to the gas in the same manner as mentioned with respect to FIG. 1.

In FIGS. 3, 4 and 5 are illustrated three apparatus for the application of the substances of FIGS. 1 or 2 to bubbles, as they are formed within the surrounding liquid.

As shown in FIG. 3, hot gas is passed through tube 30, and the coating material is passed through tube 32 which surrounds tube 30. The coating material is discharged at the same time as the gas is injected into the surrounding liquid so that an effective coating covers the bubbles as they are formed. The substance and the bubble containing fluid can also be premixed as shown in FIG. 4 and then injected through a suitable tube such as 40 into the surrounding liquid. The end of the tube may be tapered as at 41 to increase the speed of issuance of the coated bubbles, if desired. Alternatively, the coating substance is injected tangentially as illustrated in FIG. 5, to spin about the gas prior to the injection of the gas into the surrounding liquid. Thus, the coating substance is ejected from tubes 52 into main gas tube 50 to impart a spinning motion thereto. It will be appreciated that the force of the spinning motion and the angle of twist are dependent on the angle of tube 52 with respect to tube 50. For optimum conditions, this angle and relative velocities of gas and coating material should be such as to adequately spin and coat the bubbles without damaging them. The spinning motion imparts a more uniform coating to the bubbles in certain applications and also provides a more stable action to the emitting stream of coated bubbles, to prevent dissipation thereof. In other words, the spinning motion provides a tubular stream of coated bubbles emanating from tube 50 which is approximately equal in diameter thereto. Suitable pumps (not shown) may be employed to discharge either the gas or the coating material or both, as desired. It will be seen that I have described three preferred embodiments of bubble coating apparatus which are particularly suited for my invention, but it will be appreciated that there are many others which are equally well suited thereto.

It will be appreciated from the foregoing that my invention attains the objectives set forth. Because the heat dissipation properties of bubbles are substantially reduced, the life of the bubbles is increased and their usefulness is also significantly improved.

A specific embodiment of my invention has been illustrated but the invention is not limited thereto, since many modifications may be made by one skilled in the art, and the appended claims are intended to cover all such modifications as fall within the true spirit and sco e of my invention.

What I claim as new and esire to secure by Letters Patent of the United States is:

1. In a method of propulsion in which gas of one temperature is injected into water moving with respect to the point of injection thereof and at another lower temperature than said one temperature to form relatively large bubbles of gas in said water which move therewith and eventually are destroyed by forces in said water acting on said bubbles of gas to release the energy thereof to provide thrust to said water, the method of increasing the time between formation and destruction of said relatively large bubbles of gas and thereby control the time of release of the energy to optimize its effect comprising injecting a substance into said liquid medium with the injection of gas therein to form coatings of said substance about said bubbles, said substance having a boiling point and a heat of vaporization which is substantially lower than water, whereby condensation of gas within said bubbles is compensated by vaporization of said substance to maintain the pressure of gas within said bubbles relatively constant thereby increasing the time between formation and destruction thereof.

2. The combination of claim 1 in which said gas of said one temperature is steam.

3. The combination of claim 1 in which said substance is carbon tetrachloride. 

2. The combination of claim 1 in which said gas of said one temperature is steam.
 3. The combination of claim 1 in which said substance is carbon tetrachloride. 